Light emitting element housing package

ABSTRACT

A light emitting element housing package comprises a ceramic substrate on which a light emitting element is mounted, and a wiring pattern that is formed on the ceramic substrate and to which a light emitting element chip is electrically connected, wherein a white thin film layer formed from a sintered body of white inorganic particles is formed on at least an upper surface of the wiring pattern, except a connection region in the wiring pattern to be connected to the light emitting element chip.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting element housingpackage.

2. Description of the Related Art

In order to enhance efficiency in extracting light from a light emittingelement, a light emitting element housing package that houses an opticalsemiconductor light emitting element, such as an LED, has demanded atechnique for hindering a wiring pattern from absorbing light from thelight emitting element.

For instance, a proposed technique is for making a thin silver filmexhibiting a high reflectance on a surface of a wiring pattern. However,a silver thin film is likely to cause a problem, like migration oroxidative corrosion, thereby raising a problem of low reliability (seePatent Document 1) and expensiveness.

Accordingly, a technique for forming a white resist layer exhibitinghigh reflectance on a surface of a wiring pattern has already beenproposed as described in connection with Patent Document 2.

-   Patent Document 1: JP-A-2009-135536-   Patent Document 2: JP-A-2007-201171

Under the technique described in connection with Patent Document 2, asynthetic resin that is a base material of a white resist layerundergoes aged deterioration because of heat and light. Since the whiteresist layer is likely to undergo yellow discoloration, the layerencounters difficulty in maintaining a white color for a long period oftime. For this reason, there also arises a problem of efficiency inextracting light from a light emitting element being deteriorated withage.

SUMMARY OF THE INVENTION

The present invention has been conceived to solve the problem and aimsat providing a package for housing a light emitting element that makesit possible to enhance the efficiency for extracting light from a lightemitting element without involvement of aged deterioration.

As a result of having performed repeated diligent studies to solve theproblem, the present inventors came around to the following aspects ofthe present invention as mentioned below.

A first aspect of the invention provides a light emitting elementhousing package comprising a ceramic substrate on which a light emittingelement is mounted, and a wiring pattern that is formed on the ceramicsubstrate and to which a light emitting element chip is electricallyconnected, wherein a white thin film layer formed from a sintered bodyof white inorganic particles is formed on at least an upper surface ofthe wiring pattern, except a connection region in the wiring pattern tobe connected to the light emitting element chip.

According to the first aspect of the invention, since the white thinfilm is formed on at least the upper surface of the wiring pattern, itis possible to make the wiring pattern have difficulty in absorbing thelight of the light emitting element chip. The white thin filmefficiently reflects the light of the light emitting element chip, andit is possible to uniformly emit outward. Since the white thin film isformed from a sintered body of white inorganic particles, there islittle deterioration across ages by the heat or light. It is possible tokeep white color for ages. Thus, it possible to enhance the efficiencyfor extracting light from a light emitting element without ageddeterioration. Also, the white thin film does not set up a problem likemigration or oxidative corrosion and gain high reliability. It ispossible to inexpensively provide expensiveness, compared to the thinfilm of the silver.

A second aspect of the invention provides the light emitting elementhousing package, wherein the white thin film layer is made of thesintered body consisting of the white inorganic particles and inorganicbinder particles.

A third aspect of the invention provides the light emitting elementhousing package, wherein a film thickness of the white thin film layerranges from 5 to 50 μm.

The white thin film layer must be formed to a film thickness such thatthe film does not hinder superior emission of light from the lightemitting element. Specifically, when a side surface portion of a lightemission layer of the light emitting element is fully covered with thewhite thin film layer, the light originating from the light emissionlayer is blocked by the white thin film layer, so that the light cannotbe extracted.

Accordingly, a film thickness of the white thin film layer must be setin such a way that the side surface portion of the light emission layeris not fully covered with the white thin film layer.

Moreover, when the film thickness of the white thin film layer is toosmall, the white thin film layer becomes easier to let light pass, sothat the working effect yielded in connection with the first aspectcannot be yielded.

For this reason, it is desirable to set the film thickness of the whitethin film layer to 5 to 50 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross sectional view showing a generalconfiguration of a light emitting element housing package 10 of a firstembodiment embodying the present invention;

FIG. 2 is a longitudinal cross sectional view showing a generalconfiguration of a light emitting element housing package 100 of asecond embodiment embodying the present invention; and

FIG. 3 is a longitudinal cross sectional view showing a generalconfiguration of a light emitting element housing package 200 of a thirdembodiment embodying the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments embodying the present invention are hereunder described byreference to the drawings. In the embodiments, like constituent membersare given like reference numerals, and repeated explanations of the samemembers are omitted.

First Embodiment

FIG. 1 is a longitudinal cross sectional view showing a generalconfiguration of a light emitting housing package 10 of a firstembodiment. The light emitting housing package 10 is made up of aceramic substrate 11, lower electrode patterns (electrode layers) 12 and13, upper electrode patterns 14 and 15, contact holes 16 and 17, anickel (Ni) thin film layer 18, a gold (Au) thin film layer 19, wiringpatterns (wiring layers) 20 and 21, connection regions 20 a and 21 a, alight emitting element chip 22, bonding wires 23 and 24, a white thinfilm layer 25, a translucent resin layer 26, and the like.

The plate-like ceramic substrate 11 is made of inexpensive sinteredaluminum oxide (alumina ceramics).

The lower electrode patterns 12 and 13 are made of a a thick film layerof copper (Cu) and made by printing and applying Cu-containing conductorpaste over a back side of the ceramic substrate 11 through use of ascreen printing technique, or the like, and sintering the thus-printedsubstrate.

The upper electrode patterns 14 and 15 are formed from a thick copperfilm layer by means of printing and applying copper-containing conductorpaste over a top side of the ceramic substrate 11 through use of thescreen printing technique, or the like, and sintering the thus-printedsubstrate.

The contact holes 16 and 17 are formed in the ceramic substrate 11 in apenetrating fashion, so as to interconnect the front and back sides ofthe ceramic substrate 11. Cu-containing conductor paste is embedded inthe contact holes 16 and 17, and the contact holes are then sintered,whereby a copper layer is formed.

The lower electrode pattern 12 and the upper electrode pattern 14 areintegrally connected together by way of the copper layer in the contacthole 16. The lower electrode pattern 13 and the upper electrode pattern15 are integrally connected together by way of the copper layer in thecontact hole 17.

The nickel thin film layer 18 is formed so as to cover an overallsurface of the upper electrode patterns 14 and 15 and an overall surfaceof the lower electrode patterns 12 and 13, by use of an electrolyticplating technique or a nonelectrolytic plating technique.

The gold thin film layer 19 is formed so as to cover the entire surfaceof the nickel thin film layer 18 by use of the electrolytic platingtechnique or the nonelectrolytic plating technique.

The wiring pattern 20 is formed from the upper electrode pattern 14 andthe nickel thin film layer 18 and the gold thin film layer 19 that areformed over a surface of the upper electrode pattern.

The wiring pattern 21 is formed from the upper electrode pattern 15 andthe nickel thin film layer 18 and the gold thin film layer 19 that areformed over a surface of the upper electrode pattern.

The light emitting element chip 22 is implemented as a result of beingfixedly mounted on the wiring pattern 20, to thus be mounted on theceramic substrate 11.

The light emitting element chip 22 is formed from; for instance, a barechip of an optical semiconductor type light emitting element, like anLED element and an organic EL element.

A light emission layer 22 a that substantially emits light is stacked onthe light emitting element chip 22.

A positive electrode (omitted from the drawings) and a negativeelectrode (omitted from the drawings) are formed over an upper surfaceof the light emitting element chip 22.

The connection region 20 a is arranged and formed on the wiring pattern20, and the connection region 21 a is arranged and formed on the wiringpattern 21.

By use of a wire bonding technique, the positive electrode of the lightemitting element chip 22 and the connection region 20 a are electricallyconnected by means of the bonding wire 23. The negative electrode of thelight emitting element chip 22 and the connection region 21 a areelectrically connected together by means of the bonding wire 24.

The white thin film layer 25 is formed from; for instance, a sinteredbody consisting of white inorganic particles made of an aluminum oxideand inorganic binder particles made of silicon oxide. The white thinfilm layer is formed so as to cover upper surfaces of the wiringpatterns 20 and 21 except the connection regions 20 a and 21 a.

The transparent resin layer 26 is made of a transparent silicon resin, atransparent epoxy resin, or the like, so as to cover respective members(i.e., the wiring patterns 20 and 21, the light emitting element chip22, the bonding wires 23 and 24, and the white thin film layer 25)formed on the top side of the ceramic substrate 11 in a sealing fashion,and an upper surface of the transparent resin layer is formed into asubstantially spherical shape.

[Working-Effects of the First Embodiment]

The light emitting element housing package 10 of the first embodimentcan yield the working-effects, such as those provided below.

[1] The white thin film layer 25 covers the upper surfaces of the wiringpatterns 20 and 21 except the connection regions 20 a and 21 a.Therefore, it becomes possible to make the wiring patterns 20 and 21difficult to absorb light of the light emitting element chip 22, and thewhite thin film layer 25 efficiently reflects light of the lightemitting element chip 22, to thus be able to radiate the light to theoutside uniformly and excellently.

By use of a formation material to be described later, the white thinfilm layer 25 can exhibit high reflectance equal to that of a silverthin film.

[2] In the thin film layer of an organic material, like the white resistlayer described in connection with Patent Document 2, a synthetic resinthat a base material is susceptible to yellow discoloration through ageddeterioration by means of heat or light. Therefore, the synthetic resinencounters difficulty in maintaining a white color over a long period oftime, which raises a problem of deterioration of the efficiency forextracting light from the light emitting element chip 22 with age.

In contrast, since the white thin film layer 25 is made of a sinteredbody of white inorganic particles and hardly undergoes ageddeterioration, which would otherwise be caused by heat and light, andcan maintain a white color for a long period of time. Therefore, theefficiency for extracting light form the light emitting element chip 22can be enhanced without involvement of aged deterioration.

The white thin film layer 25 is free from a problem, like migration oroxidative corrosion, as in the case of a silver thin film. In additionto its high reliability, the white thin film layer can be provided lessexpensive when compared with a silver thin film, so long as a formationmaterial, which will be provided below, is used.

[3] The white thin film layer 25 is made by means of printing andapplying paste that is a mixture of white inorganic particles andinorganic binder particles for promoting sintering of the whiteinorganic particles through use of the screen printing technique, or thelike, and subsequently sintering the thus-printed paste.

It is preferable to use as the white inorganic particles; for instance,a titanium oxide, a boron nitride, a zirconium oxide, or the like, aswell as an aluminum oxide.

Further, it is preferable to use as the inorganic binder particles; forinstance, a magnesium oxide, a calcium oxide, and the like, as well as asilicon oxide.

The white thin film layer 25 is sintered at a temperature of about 500to 600° C. The present inventors experimentally ascertained that thereis no potential of the respective layers (the upper electrode patterns14 and 15, the nickel thin film layer 18, and the gold thin film layer19) making up the wiring patterns 20 and 21 being adversely affectedduring sintering operation.

[4] The white thin film layer 25 must be formed to a film thickness thatdoes not block superior light emission of the light emitting chip 22.

Specifically, when a side surface portion of the light emission layer 22a of the light emitting element chip 22 is completely covered with thewhite thin film layer 25, the light radiated form the light emissionlayer 22 a is blocked and not extracted by the white thin film layer 25.

Accordingly, the film thickness of the white thin film layer 25 must beset in such a way that the side surface portion of the light emissionlayer 22 a is not completely covered with the white thin film layer 25.

If the film thickness of the white thin film layer 25 is made too small,light will become easier to pass through the white thin film layer 25,so that the working effect described in connection with [1] will becomedifficult to yield.

Therefore, it is desirable to set the film thickness of the white thinfilm layer 25 to; for instance, 5 to 50

Second Embodiment

FIG. 2 is a longitudinal cross sectional view showing a generalconfiguration of a light emitting element housing package 100 of asecond embodiment.

The light emitting element housing package 100 is made up of the ceramicsubstrate 11, the lower electrode patterns 12 and 13, the upperelectrode patterns 14 and 15, the contact holes 16 and 17, the nickel(Ni) thin film layer 18, the gold thin film layer 19, the wiringpatterns 20 and 21, the connection regions 20 a and 21 a, the lightemitting element chip 22, the white thin film layer 25, the transparentresin layer 26, bumps 101 and 102, and the like.

The light emitting element housing package 100 of the second embodimentdiffers from the light emitting element housing package 10 of the firstembodiment in only that the light emitting chip 22 is flip-chip mountedby use of the bumps 101 and 102.

Specifically, the positive electrode of the light emitting chip 22 andthe connection region 20 a are electrically connected together by meansof the bump 101. The negative electrode of the light emitting elementchip 22 and the connection region 21 a are electrically connectedtogether by means of the bump 102.

The bumps 101 and 102 are made of; for instance, gold, solder, or thelike.

Even the second embodiment also yields working effects identical withthe working effects [1] to [4] described in connection with the firstembodiment.

Third Embodiment

FIG. 3 is a longitudinal cross sectional view showing a generalconfiguration of a light emitting element housing package 200 of a thirdembodiment.

The light emitting element housing package 200 is made up of the ceramicsubstrate 11, the lower electrode patterns 12 and 13, the upperelectrode patterns 14 and 15, the contact holes 16 and 17, the nickelthin film layer 18, the gold thin film layer 19, the wiring patterns 20and 21, the connection regions 20 a and 21 a, the light emitting elementchip 22, bonding wires 23 and 24, the white thin film layer 25, thetransparent resin layer 26, a reflector 201, and the like.

The light emitting element housing package 200 of the third embodimentdiffers from the light emitting element housing package 10 of the firstembodiment in only that the reflector 201 is provided.

The reflector 201 is made of a synthetic resin, ceramics, and the like,and fixedly mounted on the front side of the ceramic substrate 11 so asto surround the respective members (the wiring patterns 20 and 21, thelight emitting element chip 22, the bonding wires 23 and 24, and thewhite thin film layer 25).

In the reflector 201, an inner peripheral surface of a recess 201 aforms a slope that is inclined toward an aperture 201 b. The reflectorreflects light from the light emitting chip 22, to thus be able toefficiently emit the light from the aperture 201 b.

The recess 201 a of the reflector 201 is filled with the transparentresin layer 26.

Even the third embodiment yields working effects identical with theworking effects [1] to [4] described in connection with the firstembodiment.

In the third embodiment, the light emitting element chip 22 may also beflip-chip mounted in the same way as in the second embodiment.

The present invention shall not be limited to descriptions about therespective phases and the embodiments. Various deformations of theembodiments shall also fall within the scope of the present inventionwithout departing descriptions of the appended claims to an extent thatthe skilled in the art can readily conceive the deformations. Alldetails of theses, unexamined patent publication bulletins, patentpublications, or the like, referred to in the present patentspecification are cited by reference.

1. A light emitting element housing package comprising: a ceramicsubstrate on which a light emitting element is mounted; and a wiringpattern that is formed on the ceramic substrate and to which a lightemitting element chip is electrically connected, wherein a white thinfilm layer formed from a sintered body of white inorganic particles isformed on at least an upper surface of the wiring pattern, except aconnection region in the wiring pattern to be connected to the lightemitting element chip.
 2. The light emitting element housing packageaccording to claim 1, wherein the white thin film layer is made of thesintered body consisting of the white inorganic particles and inorganicbinder particles.
 3. The light emitting element housing packageaccording to claim 1, wherein a film thickness of the white thin filmlayer ranges from 5 to 50 μm.